1. Field of the Invention
The present invention relates to a radio frequency input circuit with an electrostatic discharge (ESD) protection function, for use in telecommunications devices.
2. Description of the Related Art
In general, cases in which an electrostatic discharge (ESD) having a high electric potential is instantaneously introduced into a portable telecommunications device (hereinafter, referred to as telecommunications devices) such as a smart phone through input terminals as users frequently contact portable devices, and thus, portable devices need to have an ESD protection function.
In existing telecommunications devices, a radio frequency input circuit includes an ESD protection circuit provided between a connection node between an input terminal and a DC blocking capacitor, and a ground.
In a case in which an ESD voltage is input through the input terminal, the ESD protection circuit forms a discharge path for the ESD voltage to allow the ESD voltage to flow to the ground. This operation may protect the DC blocking capacitor from the ESD voltage.
In this regard, the ESD protection circuit includes a forward diode circuit unit including a plurality of diodes connected to each other in series in a forward direction to form an ESD protection path for a positive (+) ESD voltage and a backward diode circuit unit including a plurality of diodes connected to each other in series in a backward direction to form an ESD protection path for a negative H) ESD voltage.
However, there may be a problem such as increasing a size of an ESD protection circuit according to the related art, since the higher the voltage level of an input signal becomes, the more the number of the diodes need to be connected to each other in series in such a manner that the ESD protection circuit does not operate at a voltage of the input signal but only operates at the ESD voltage.
Also, parasitic capacitance may occur to correspond to the number of diodes used for the ESD protection circuit, and thus, impedance mismatching is likely to occur, and an additional protection circuit is problematically necessary for compensating for the impedance mismatching.
The Related Art document below relates to a noise filter and a noise filter embedded amplifier circuit and does not disclose the matter for improving a defect in that the higher the voltage level of the input signal becomes, the more the size thereof increases.